1. Field of the Invention
The invention generally relates to an optical engine, and more particularly, to an optical engine providing both a visible image beam and an invisible beam.
2. Description of Related Art
Generally speaking, a projection apparatus projects images produced by a light valve therein onto a screen. By adopting an infrared light source and an optical detector, a projection apparatus may further achieve an image detection function besides the original image projection function. Accordingly, a touch screen function may be further achieved by the projection apparatus.
To be specific, a projection apparatus with the touch screen function usually has an optical engine, a plurality of charge coupled devices (CCDs), and an infrared light emitting system. The optical engine provides an image beam, wherein the image beam is projected onto a screen located at an object side to form an image. The infrared light emitting system provides an infrared beam, wherein the infrared beam is transmitted towards the object side, and part of the infrared beam passes through the screen. Thus, when an object (for example, a finger) from the object side reaches the screen, the part of the infrared beam passing through the screen is reflected by the object to form an object beam, and the object beam is then transmitted to the CCDs. Accordingly, the CCDs may detect the image of the object.
In a conventional projection apparatus with the touch screen function, the image beam and the infrared beam do not share the same transmission path, and the transmission paths thereof are independent from each other. Accordingly, the space efficiency of the optical engine, the CCDs, and the infrared light emitting system is very low, and the volume of the projection apparatus may not be reduced. Besides, since the transmission paths of the image beam and the infrared beam are independent from each other, the positions of the optical engine, the CCDs, and the infrared light emitting system are difficult to be corrected.
In addition, the infrared beam emitted by the infrared light emitting system has to be shaped by a beam shaping element in order to irradiate every area on the screen, and even so, the infrared beam may not be uniformly projected onto the screen. As a result, the light intensity of the infrared beam within some areas on the screen may be higher than that within some other areas on the screen. Thus, a plurality of CCDs has to be disposed in the conventional projection apparatus, and these CCDs have different gains. The CCD having a greater gain is used for detecting an area having a lower light intensity on the screen, and the CCD having a smaller gain is used for detecting an area having a higher light intensity on the screen.
In other words, if only one CCD is adopted, there is only one gain. As a result, images produced on the CCDs within those areas having higher light intensities on the screen may be oversaturated while images produced on the CCDs within those areas having lower light intensities may be too dark to be identified. However, the structure of the projection apparatus may become too complicated and bulky if a plurality of CCDs are adopted.
In another conventional projection apparatus with the touch screen function, red light, green light, blue light, and infrared light are sequentially projected onto a light valve, and an image beam and an infrared beam are then transmitted to the object side through the light valve. However, because the light valve has to process the infrared light during a period time, the algorithm for controlling the light valve becomes very complicated and accordingly the cost of the projection apparatus is increased. Besides, the light valve may have enough time for processing the infrared light in order to allow the CCDs to identify the infrared beam. However, this may shorten the time for the light valve to process the visible lights, and accordingly the brightness of the image provided by the projection apparatus may be reduced. In addition, because the time for processing the infrared light is only part of the total processing time of the light valve, the identification of the CCDs to an object at the object side may not be improved.